In an excimer lamp, an arc tube, which serves as dielectrics, is arbitrarily filled up with light emission gas and halogen, wherein excimer molecules are generated in the arc tube by dielectric barrier discharge, so that excimer light is emitted from the excimer molecules. Such a lamp is used as an ultraviolet ray light source for photochemical reactions. In such an excimer lamp, rare gas (argon, krypton, xenon, etc.) and fluorine are enclosed as an electric discharge gas depending on the wavelength of excimer light to be obtained.
FIG. 11 is a table showing the relation of combinations of rare gas and fluorine and radiation wavelength. Light having wavelength shown in the table is used for a surface alteration and sterilization. Specifically, an excimer lamp, in which argon-fluorine or krypton-fluorine is enclosed and emission of light whose wavelength is 193 nm or 248 nm can be obtained, is widely used for lithography, and a wide variety of fields, such as a characteristic test of a photo-sensitive film, circumference exposure, and a mask examination.